This invention relates to digitizing tablets and, more particularly, to a combined display and digitizing input device for a computer comprising, a graphics display panel; a first grid of parallel transparent conductors disposed over a surface of the display panel; and, a second grid of parallel transparent conductors disposed over the first grid of parallel transparent conductors electrically insulated therefrom and perpendicular thereto.
Digitizing tablets have been available as inputting devices for use with computers for a number of years. Traditionally, they have been used for digitizing drawings and for inputting to CAD/CAM, desktop publishing systems, and the like. In the typical prior art digitizing tablet system, the tablet itself contains an X-grid of wires and a Y-grid of wires perpendicular thereto. A stylus device is moved over the surface of the tablet and the position of the stylus device is sensed in the X and Y coordinate system defined by the X and Y grids of wires by interaction between the stylus device and the grids of wires. Most typically, the interaction is electromagnetic or electrostatic.
More recently, digitizing tablets have gained greatly in importance in their association with computers as the primary input device in so-called pen-driven computing systems. In such systems, the digitizing tablet is associated with a display panel as depicted in FIG. 1 and the combination is employed in the manner of early "light pens" and cathode ray tube (CRT) displays wherein displayed choices on the CRT could be selected by placing a light-sensing pen against the face of the CRT. In those prior art CRT/light pen systems, the selection made by the user could be determined by the point in the raster scanning pattern where the electron beam creating the display was sensed by the light pen. By replacing the CRT with a liquid crystal display (LCD) panel 10 and the light pen with a digitizing tablet 12, a lightweight and portable input device is created. Thus, as shown in FIG. 1, a menu 14 can be displayed on the LCD panel 10 and individual items 16 in the menu 14 can be selected by employing the stylus 18. As can be appreciated, the potential for such devices and pen-driven computing in combination for various applications is virtually boundless.
The pen-driven LCD/digitizer input devices presently commercially available in the prior art are of several types. One operates electrostatically and the others operate electromagnetically. The electrostatic device is made by Scriptel and its manner of operation is depicted in FIGS. 2 and 3. The digitizing portion 60 comprises a sheet of glass 62 having a layer of indium tin oxide (ITO) 64 disposed over the bottom surface thereof. The digitizing portion 60 is then positioned over the LCD panel 10. The stylus 18 is moved over the surface of the glass 62. The glass 62 is, of course, a dielectric layer and it electrically separates the stylus 18 from the ITO layer 64. The ITO layer 64 is transparent and resistively conductive. The ITO layer 64 is connected at its edges to electrostatic drivers 66, 66' for each of the directions of the coordinate system associated with the digitizing portion 60. The location of the stylus 18 in the X or Y direction can be determined as follows. First, an electrostatic signal is applied by the driver 66. The signal sensed by the stylus 18 is a function of the resistance R.sub.1. Next, an electrostatic signal is applied by the driver 66'. The signal sensed by the stylus 18 in this case is a function of the resistance R.sub.2. The position of the stylus 18 can then be determined using interpolative techniques as a function of the differences in the electrostatic signals sensed by the stylus 18 caused by the differences in the resistances R.sub.1 and R.sub.2. The Scriptel device is not cordless (i.e. there is a connecting cable between the stylus 18 and the digitizing portion 60) as is desired in pen-driven LCD/digitizer input devices. Also, it is subject to the problems of electrostatically operating digitizers such as moisture and hand effects.
The electromagnetic devices as built by companies such as CalComp (the assignee of this application), Wacom, Kurta, and Numonics employ a grid structure placed below the LCD/backlight assembly as shown in simplified functional cross section in FIG. 4. All of the foregoing with the exception of the Numonics device are cordless. The top surface over which the stylus 18 is moved is the LCD panel 10. Below the LCD panel 10 is a backlighting panel 20 which illuminates the LCD panel 10 for easy viewing. Finally, the digitizing grids 22 are placed below the backlighting panel 20. Positional sensing of the stylus 18 is accomplished by the use of electromagnetic fields which exist between the stylus 18 and the digitizing grids 22 in any manner well known to those skilled in the art. Because of this structure, there are limitations on the placement of components, the digitizing technology, and its performance. An LCD panel of the type having a printed circuit board across its back surface carrying associated driving components cannot be employed as the metal of the printed circuit board will interfere with the electromagnetic fields and render the digitizing apparatus inoperative. The Scriptel (electrostatic) device, of course, does not have this problem since any printed circuit board associated with the LCD panel is not positioned between the transmitting and receiving components. Because of the distances and the electrostatic fields associated with the LCD panel 10 and the backlighting panel 20, the prior art electromagnetic approaches may also suffer from jitter and other problems.
Another major consideration is thickness. Every manufacturer of pen-driven LCD/digitizer input devices would like to be able to supply a zero (0) thickness tablet and, therefore, a zero (0) thickness digitizer. All present electromagnetic digitizers, however, require at least 0.1 inch of thickness for their grid assembly.
Wherefore, it is an object of the present invention to provide an LCD panel in combination with a digitizing tablet for use in pen-driven computing applications where the tablet employs electromagnetic sensing, sensitivity is maximized, and problems caused by adjacent electrostatic fields are virtually eliminated.
It is another object of the present invention to provide an LCD panel in combination with a digitizing tablet for use in pen-driven computing applications where any type of LCD panel can be employed.
It is still another object of the present invention to provide a transparent digitizing grid system which can be disposed over the surface of an LCD panel without interfering with the viewing of a display on the panel.
It is yet another object of the present invention to provide a transparent digitizing grid system which can be disposed over the surface of an LCD panel wherein the grid assembly is of a thickness of approximately 0.020 inch so as to approach a zero (0) thickness.
It is a further object of the present invention to provide an LCD panel in combination with a digitizing tablet for use in pen-driven computing applications where the tablet employs electromagnetic sensing, the LCD panel can be mounted on a printed circuit board, and the printed circuit board is not disposed between transmitting and receiving portions of the digitizing tablet.
Other objects and benefits of the invention will become apparent from the detailed description which follows hereinafter when taken in conjunction with the drawing figures which accompany it.